Background of the antigen
Fukutin, a secreted protein, is expressed in various tissues in normal individuals. Fukutin colocalizes with a Golgi marker and a granular cytoplasmic distribution, suggesting that fukutin passes through the Golgi before being packaged into secretory vesicles. Fukutin may be located in the extracellular matrix, where it interacts with and reinforces a large complex encompassing the outside and inside of muscle membranes; alternatively, as a secreted protein, fukutin may cause muscular dystrophy by an unknown mechanism. The fukutin gene is expressed at similar levels in control fetal and adult brain, but is much reduced in Fukuyama congenital muscular dystrophy (FCMD) brains. Fukutin deficiency affects the modification of glycosylation of DAG1 (α-dystroglycan), which then cannot localize or function properly and may be degraded or eluted from the extracellular surface membrane of the muscle fiber. FCMD is the first human disease known to be caused by an ancient retrotransposal integration. The gene which encodes fukutin maps to human chromosome 9q31.
